1. Field of the Invention
The present invention pertains to universal joints for use in drive train, power steering, and power transmission systems. More particularly, the present invention pertains to a bearing cup for a universal joint. Even more particularly, the present invention pertains to a lubricant impregnated bearing cup for a universal joint.
2. Description of the Prior Art
Universal joints are well known devices for transferring rotational movement between two members adapted to rotate about non-aligned axes of rotation. They are widely used to connect rotatable members in vehicular drive train and steering systems.
A typical drive train system for a rear-wheel drive vehicle comprises an output shaft extending from the transmission to a driveshaft. The output shaft is connected to a first end of the driveshaft via a first universal joint. A second universal joint connects a second end of the driveshaft to the vehicle's rear axle assembly. The two universal joints accommodate a limited amount of misalignment between the drive train components.
In steering systems, universal joints are used to connect the steering column to the pinion in a rack-and-pinion steering system.
Generally, the structure of a universal joint includes a cross assembly having a central body portion from which a plurality of trunnions outwardly extend. The trunnions are coplanar and are positioned at substantially equal angles relative to each other. Universal joints typically comprise three or four trunnions positioned about the body portion.
A hollow cylindrical bearing cup having a closed end and an open end is mounted on the end of each of the trunnions. A first opposed pair of bearing cups is connected about their cylindrical circumference to a first yoke which is coupled with the output shaft. The bearing cups mounted on the second opposed pair of trunnions are secured about their cylindrical circumference to a second yoke which is connected to the driveshaft.
As the drive train or steering system is operated, the driveshaft or steering column, respectively, is rotated. As rotation occurs about the output shaft, the universal joint is rotated, thus transferring the rotational energy to the drive shaft connected to the universal joint. As the output and drive shafts rotate, the bearing cups and trunnions may experience an angular displacement, or rotational movement, relative to each other as well. Although the output and drive shafts may experience a high rate of rotational speed, the rotation between the bearing cups and the trunnions may be minimal. The rotational motion between the bearing cup and the trunnion is angular and oscillatory, completing one full cycle per shaft revolution. Therefore, the rate of angular rotation between the bearing cups and the trunnions is sinusoidal and a function of the rate of the output shaft and the drive shaft rotation and the angle of misalignment between the output shaft and the drive shaft.
When a universal joint is transmitting a torsional load, the trunnion exerts a compression force upon the interior of the bearing cup. The compression force is a function of the torque transmitted about the universal joint.
Oftentimes, mechanical bearings, such as needle bearings, are positioned between an inner surface of the bearing cup and an outer surface of the trunnion to facilitate rotational movement between the trunnions and the bearing cups. The needle bearings require lubrication to ensure that they do not wear down unevenly and at an accelerated rate. In lieu of needle bearings, roller or ball elements may be used for mechanical bearing purposes.
However some bearing cups do not require mechanical bearings, as is described in U.S. Pat. No. 4,758,202 to Maciag et al. Nonetheless, all bearing cups require lubrication to reduce friction caused by the relative motion between the inner bearing cup surface and the outer trunnion surface.
When the universal joint is under a torsional load, each trunnion exerts a varying cyclical compressive force upon the interior of its respective bearing cup. The location of this force is along the contact surface between the bearing cup and the trunnion. The force varies in an oscillatory fashion as the bearing cup and the trunnion experience angular displacement relative to each other.
A conventional bearing cup which lacks sufficient lubrication can lead to premature system failure. To alleviate this, bearing cups often have a seal disposed at the open end of the cup to ensure that lubricant does not leak out of the bearing cup and around the trunnion. The seal also serves to prevent moisture, dirt, and other foreign matter from entering the bearing cup and contaminating the working surfaces, which can cause premature failure, as well.
During use, the lubricant comes under pressure, and it will often seep from the bearing cup. The bearing cup seal initially resists the lubricant from exiting the bearing cup. However universal joint seals are subjected to extreme environmental conditions in which aging is accelerated and cracks develop, leading to increased leakage of lubricant.
In the case of an impregnated powder metal bearing cup, as is described in U.S. Pat. No. 4,758,202 to Maciag et al., the cyclical compressive forces that occur as the bearing rotates, under load, back and forth on the trunnion, create a pumping action that causes the impregnated lubricant to dry out at the trunnion-bearing interface and weep from all of the exposed bearing surfaces. Consequently this causes failure of the internal components of the bearing cup, and eventually complete failure of the universal joint.
In addition to problems resulting from insufficient lubricant, universal joints are also subject to vibration-related issues. Systems that employ universal joints are comprised of a number of moving parts. Variations in manufacturing tolerance control can lead to shock, vibration, and noise which are transmitted throughout the entire system. This can cause an unacceptable annoyance to the vehicle operator and passengers, and can result in the ultimate failure of the universal joints.
The present invention, as is detailed herein below, seeks to solve these issues by providing an improved bearing cup which minimizes lubricant leakage. In addition, the present invention significantly reduces the transmission of shock, vibration, and noise from a first drive shaft to a second drive shaft.